Although optical waveguides, such as optical fibers, have been designed for delivering light over long distances with little attenuation in the intensity of the light, there are many applications in which it is desirable that light also be extracted from the waveguide at various points along its length. There are two types of extraction: directed and diffuse.
Directed extraction methods provide extracted light in a particular desired direction. A variety of structures for directed light extraction, many of which use prisms, have been developed. These extractors are particularly useful for applications requiring, for example, light to be directed toward a particular point or object.
Diffuse light extraction methods provide light that is directed over a range of directions. There are a variety of applications that require diffuse rather than directed light. Such applications range from lighted display signs to lamps for offices or other workplaces. Neon lighting has been used for these applications. However, optical waveguides with diffuse light extractors have several advantages over neon lighting. For example, the optical waveguide typically uses a low voltage light source as opposed to the neon light which requires high voltage for operation. Importantly, optical waveguides can use a variety of light sources including incandescent and electrical arc sources, that may be more energy efficient than neon. Furthermore, the optical waveguide can provide light of any desired color by using an appropriately colored light source or light filter. The color can be easily changed by changing the light source or filter. Neon lighting, on the other hand, requires either a particular choice of gas or phosphor coatings in the tubing of the neon lighting or, alternatively, the use of colored translucent glass tubing. Finally, neon lighting is made of glass which is rigid and cannot be subsequently adapted to alterations in the desired lighting design. Optical waveguides, on the other hand, can be made from flexible and durable materials which can be altered to form a variety of different configurations depending on the need.
While there are many advantages to using optical waveguides and diffusional light extractors, progress in this field has been slow. Existing products show that the industry has long struggled, with little success, to provide a practical design that is also efficient.